简易计算器的实现

xml布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.app.MainActivity" >
    <EditText 
        android:id="@+id/editText_1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:editable="false"
        android:gravity="right"
        />
    <Button 
        android:id="@+id/delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:text="删除"
        android:textSize="20sp"
        />
    <LinearLayout 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
     >
        <LinearLayout 
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:gravity="center_horizontal"
          >
            <Button 
                android:id="@+id/btn_7"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="7"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_8"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="8"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_9"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="9"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/divide"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="/"
                android:textSize="20sp"
                />
        </LinearLayout>
        <LinearLayout 
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:gravity="center_horizontal"
          >
            <Button 
                android:id="@+id/btn_4"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="4"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_5"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="5"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_6"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="6"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/multiply"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="*"
                android:textSize="20sp"
                />
        </LinearLayout>
        <LinearLayout 
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:gravity="center_horizontal"
          >
            <Button 
                android:id="@+id/btn_1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="1"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="2"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="3"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/del"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="-"
                android:textSize="20sp"
                />
        </LinearLayout>
        <LinearLayout 
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:gravity="center_horizontal"
          >
            <Button 
                android:id="@+id/point"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="."
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/btn_0"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="0"
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/equals"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="="
                android:textSize="20sp"
                />
            <Button 
                android:id="@+id/add"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="+"
                android:textSize="20sp"
                />
        </LinearLayout>
    </LinearLayout>
</LinearLayout>

源程序：
package com.example.app;

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity implements OnClickListener{
    
    private Button delete;
    private Button btn_1;
    private Button btn_2;
    private Button btn_3;
    private Button btn_4;
    private Button btn_5;
    private Button btn_6;
    private Button btn_7;
    private Button btn_8;
    private Button btn_9;
    private Button point;
    private Button divide;
    private Button multiply;
    private Button add;
    private Button del;
    private EditText editText;
    private Button equals;
    private Button btn_0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText = (EditText) findViewById(R.id.editText_1);
        delete = (Button) findViewById(R.id.delete);
        btn_0 = (Button) findViewById(R.id.btn_0);
        btn_1 = (Button) findViewById(R.id.btn_1);
        btn_2 = (Button) findViewById(R.id.btn_2);
        btn_3 = (Button) findViewById(R.id.btn_3);
        btn_4 = (Button) findViewById(R.id.btn_4);
        btn_5 = (Button) findViewById(R.id.btn_5);
        btn_6 = (Button) findViewById(R.id.btn_6);
        btn_7 = (Button) findViewById(R.id.btn_7);
        btn_8 = (Button) findViewById(R.id.btn_8);
        btn_9 = (Button) findViewById(R.id.btn_9);
        point = (Button) findViewById(R.id.point);
        divide = (Button) findViewById(R.id.divide);
        equals = (Button) findViewById(R.id.equals);
        multiply = (Button) findViewById(R.id.multiply);
        add = (Button) findViewById(R.id.add);
        del = (Button) findViewById(R.id.del);
        btn_0.setOnClickListener(this);
        btn_1.setOnClickListener(this);
        btn_2.setOnClickListener(this);
        btn_3.setOnClickListener(this);
        btn_4.setOnClickListener(this);
        btn_5.setOnClickListener(this);
        btn_6.setOnClickListener(this);
        btn_7.setOnClickListener(this);
        btn_8.setOnClickListener(this);
        btn_9.setOnClickListener(this);
        add.setOnClickListener(this);
        delete.setOnClickListener(this);
        del.setOnClickListener(this);
        multiply.setOnClickListener(this);
        equals.setOnClickListener(this);
        divide.setOnClickListener(this);
        point.setOnClickListener(this);
    
    }

    @Override
    public void onClick(View v) {
        String text = editText.getText().toString();
        switch(v.getId()){
        case R.id.btn_0:
        case R.id.btn_1:
        case R.id.btn_2:
        case R.id.btn_3:
        case R.id.btn_4:
        case R.id.btn_5:
        case R.id.btn_6:
        case R.id.btn_7:
        case R.id.btn_8:
        case R.id.btn_9:
        case R.id.point:
            editText.setText(text+((Button) v).getText());
            break;
        case R.id.add:
        case R.id.del:
        case R.id.multiply:
        case R.id.divide:
            editText.setText(text+" "+((Button) v).getText()+" ");
            break;
        case R.id.delete:
            if(text!=null&&!text.equals(""))
            editText.setText(text.substring(0, text.length()-1));
            break;
        case R.id.equals:
            getResult();
            break;
            
        }
    }
    private void getResult(){
        String text = editText.getText().toString();
        if(text==null||text.equals(" ")){
            return;
        }
        if(!text.contains(" ")){
            return;
        }
        double result;
        String s1 = text.substring(0, text.indexOf(" "));
        String oprate = text.substring(text.indexOf(" ")+1, text.indexOf(" ")+2);
        String s2 = text.substring(text.indexOf(" ")+3);
        
        if(!s1.equals("")&&!s2.equals("")){
            double d1 = Double.parseDouble(s1);
            double d2 = Double.parseDouble(s2);
            if(d1==0){
                if(oprate.equals("+")){
                    result = d2;
                    if(!s1.contains(".")&&!s2.contains(".")){
                        editText.setText((int)result+"");    
                    }
                    editText.setText(result+"");
                }
                if(oprate.equals("*")){
                    result = 0;
                    
                    editText.setText(result+"");
                }
                if(oprate.equals("/")){
                    result = 0;
                    
                    editText.setText(result+"");
                }
                if(oprate.equals("-")){
                
                    result = 0-d2;
                    
                    editText.setText(result+"");
                }
            }
            if(oprate.equals("+")){
                result = d1+d2;
                if(!s1.contains(".")&&!s2.contains(".")){
                    editText.setText((int)result+"");    
                }
                editText.setText(result+"");
            }
            if(oprate.equals("*")){
                result = d1*d2;
                
                editText.setText(result+"");
            }
            if(oprate.equals("/")){
                result = d1/d2;
                
                editText.setText(result+"");
            }
            if(oprate.equals("-")){
            
                result = d1-d2;
                
                editText.setText(result+"");
            }
        }
        
    }
}